1. Field of the Invention
The present invention relates to cutter bit holder assemblies for mining machines and, more specifically, relates to such holder assemblies which are adapted to hold two cutter bits.
2. Description of the Prior Art
In the operation of continuous mining machines, it has been known to provide cutter drum members to which a plurality of cutter bits are secured in such fashion that rotation of the cutter drum will cause the cutter bits to engage the bedded mineral material in order to free the same. Various mountings, spacings and cutter bit designs have been known.
It has been considered advantageous to equip the revolving drum member with fewer bits and wider spaces between bits so as to reduce the power required to sever the bedded mineral material, such as coal, as fewer bits are being driven into the mineral face and the amount of dust generated is reduced. It has also been suggested that many bits with relatively narrow spacing should be employed so that if a bit is lost or damaged the adjacent bits will be sufficiently close together that the machine will still cut satisfactorily and the uncut coal will not damage the drum or the bit holders.
U.S. Pat. No. 4,068,897 discloses a cutter drum assembly having a plurality of bit holders which are replaceable and each of which contains one cutter bit.
U.S. Pat. No. 2,521,089 discloses a mining machine cutter bit holder which is adapted to hold a unitary cutter bit having several cutter segments.
U.S. Pat. No. 3,834,764 discloses core breaker means for a mining machine wherein a pair of auxiliary core cutting members is positioned adjacent to the principal cutting means.
U.S. Pat. No. 3,614,164 discloses a receptacle for facilitating replacement of cutter bits. A pair of bit holders, which are disposed at different angular positions with respect to each other, is shown.
U.S. Pat. No. 3,325,219 discloses a cutting drum having a plurality of holders provided with two or three cutting bits which are so oriented and spaced from each other as to provide a furrow without encountering repeated depth-cutting. In connection with holders which have three picks it is stated that two of the picks have the same radial projection in order that one may serve as a replacement if the other is broken.
It has also been known to mount cutter bits on chains used to sever a bedded mineral.
There remains a very substantial need for a cutter bit assembly which provides an effective means for permitting cutter holder design and bit geometry and placement to optimize spacing of bit holders while minimizing the risk of damage to the cutter drum, holders, or chains during operation.